The basic concept of the Stirling engine dates back to the developments of Robert Stirling in 1817. Over the years, numerous applications for the Stirling engine have been investigated and evaluated. For example, one potential use of the Stirling engine is in automobiles and the like as a prime mover. In addition, the Stirling engine may be used as an engine power unit for hybrid electric applications. Other potential applications are the use of the Stirling engine as an auxiliary power unit and the use of the Stirling engine in marine applications and solar energy conservation applications.
Stirling engines have a reversible thermodynamic cycle and therefore can be used as a means of delivering mechanical output energy from a source of heat, or acting as a heat pump through the application of mechanical input energy. Using various heat sources, mechanical energy can be delivered by the engine. This energy can be used to generate electricity or be directly mechanically coupled to a load.
One of the disadvantages of current Stirling engines is their inefficiency due to the presence of dead volume of a working gas and the overall volumetric size of a burner device of the heat exchanging assembly. A heat transfer system utilizes heat transfer from the burner device to the working gas to cause a piston to be displaced as the working gas expands under heat and then compresses (contracts) upon cooling of the working gas. One conventional burner device is an apparatus in which air and fuel are injected into the burner device and then ignited to cause heat to be generated. The working gas is carried within a plurality of heater tubes, which are positioned proximate to the burner device so that heat is transferred from the burner device to the working gas flowing within the heater tubes.
One end of each heater tube is in communication with a piston chamber which houses one or more pistons and the heated, expanded working gas causes displacement of the one or more pistons within the piston cylinder. The one or more pistons are operatively connected to other working mechanical components for moving a drive member, such as a crankshaft, to cause mechanical energy to be delivered by the engine.
Because a single burner device is used to generate and effectuate heat transfer to the working gas flowing within a number of heater tubes, heat is often not evenly distributed to the working gas within the heater tubes. The burner device in conventional devices often has a length of 14 inches or greater for a 3-kilowatt Stirling engine and the length of each heater tube from the piston cylinder to a point proximate to the burner device is about 6 inches or more. The gas therefore must travel 6 inches up the heater tube and then 6 inches back down the heater tube to the piston cylinder after it has been heated. The associated disadvantage of such a system is that conventional heater tubes usually contain a dead volume of working gas. This refers to the volume of working gas that has not moved out of the heater tube during the expansion/compression combustion process. In other words, this constitutes a volume of stagnant working gas. This results in inefficient heat transfer from the burner device to the working gas and in turn leads to inefficient operation of the Stirling engine itself.
In addition, due to the typical size of the burner device, the burner device first heats a significant volume of air before heat transfer occurs to the working gas. This results in a considerable amount of energy being consumed before the working gas is heated and as a result, the working gas is exposed to less heat due to the inefficiencies of the burner device. In other words, a lot of the heat produced by the burner device does not get transferred to the working gas.
Accordingly, there is a continuing need to design a more efficient heat transfer manifold for use in a Stirling engine.